The present invention relates to multifrequency electro-acoustic transducers of the "Tonpilz" type having a plurality of pass bands, and a process for the construction of such transducers. Such transducers may be sonars.
In a patent application filed previously in France under No. 82/08.321 (corresponding to U.S. patent application Ser. No. 510,177), now abandoned there has been described a process for the construction of transducers of the Tonpilz type which allows high power sonal transmitters to be obtained which can transmit in two low frequency ranges separated by a difference higher than an octave.
The transducers described in that previous application are intended to transmit in a first range of low frequency fb which corresponds to the first longitudinal mode of vibration. This is a mode of vibration which corresponds to a system of stationary waves having a single node situated towards the centre of the stack of piezo-electric ceramic plates of the transducer, an antinode situated at the horn of the transducer, the vibrational amplitude of which is thus a maximum, and an antinode situated towards the countermass of the transducer. When this transducer is used to transmit on higher frequencies, the system of stationary waves is deformed and the antinodes of the system of stationary waves come close to one another. Also, one or several antinodes become located within the stack of piezo-electric creamic plates. In this case the amplitude of vibration of the horn becomes weaker.
The ceramic plates which are situated between two antinodes are deformed in phase opposition to the ceramic plates which are situated symmetrically on both those sides of the two antinodes which lie outside the region between the two antinodes. The effects of these phase-opposed plates oppose one another, so that the output of the transducer decreases when it is used at higher frequencies.